perf(core): avoid cloning unchanged log fields

Author: carderne

packages/core/src/logger.ts

@@ -322,33 +322,44 @@ function filterKeys(obj: unknown, keys: Set<string>, depth = 0): any {
 
   if (Array.isArray(obj)) {
     const isTruncated = obj.length > MAX_ARRAY_LENGTH;
-    const items = (isTruncated ? obj.slice(0, MAX_ARRAY_LENGTH) : obj).map((item) =>
-      filterKeys(item, keys, depth + 1)
-    );
+    const length = isTruncated ? MAX_ARRAY_LENGTH : obj.length;
+    let filteredItems: unknown[] | undefined = isTruncated ? [] : undefined;
+
+    for (let index = 0; index < length; index++) {
+      const item = obj[index];
+      const filteredItem = filterKeys(item, keys, depth + 1);
+
+      if (filteredItems) {
+        filteredItems.push(filteredItem);
+      } else if (filteredItem !== item) {
+        filteredItems = obj.slice(0, index);
+        filteredItems.push(filteredItem);
+      }
+    }
 
     if (isTruncated) {
-      items.push(`[truncated ${obj.length - MAX_ARRAY_LENGTH} more items]`);
+      filteredItems!.push(`[truncated ${obj.length - MAX_ARRAY_LENGTH} more items]`);
     }
 
-    return items;
+    return filteredItems ?? obj;
   }
 
-  const filteredObj: any = {};
+  let filteredObj: Record<string, unknown> | undefined;
 
   for (const [key, value] of Object.entries(obj)) {
-    if (keys.has(key.toLowerCase())) {
-      if (value) {
-        filteredObj[key] = `[filtered ${prettyPrintBytes(value)}]`;
-      } else {
-        filteredObj[key] = value;
-      }
-      continue;
+    const filteredValue = keys.has(key.toLowerCase())
+      ? value
+        ? `[filtered ${prettyPrintBytes(value)}]`
+        : value
+      : filterKeys(value, keys, depth + 1);
+
+    if (filteredValue !== value) {
+      filteredObj ??= { ...(obj as Record<string, unknown>) };
+      filteredObj[key] = filteredValue;
     }
-
-    filteredObj[key] = filterKeys(value, keys, depth + 1);
   }
 
-  return filteredObj;
+  return filteredObj ?? obj;
 }
 
 function truncateString(value: string): string {

packages/core/test/logger.test.ts

@@ -208,4 +208,27 @@ describe("redact()", () => {
 
     expect(result.connectionString).toMatch(/^\[filtered/);
   });
+
+  it("preserves references when no values need redaction or truncation", () => {
+    const nested = { keep: "this stays" };
+    const value = { nested, values: ["one", "two"] };
+
+    const result = redact(value);
+
+    expect(result).toBe(value);
+    expect((result as typeof value).nested).toBe(nested);
+    expect((result as typeof value).values).toBe(value.values);
+  });
+
+  it("returns a redacted copy without mutating the input", () => {
+    const nested = { token: "secret" };
+    const value = { nested };
+
+    const result = redact(value) as typeof value;
+
+    expect(result).not.toBe(value);
+    expect(result.nested).not.toBe(nested);
+    expect(result.nested.token).toMatch(/^\[filtered/);
+    expect(nested.token).toBe("secret");
+  });
 });